1. Field of the Invention
The present invention relates to a display device such as an organic EL (electroluminescence) display device, inorganic EL display device, liquid crystal display device, or plasma display device.
2. Description of Related Art
Display devices like an organic EL display device provided with a self-luminous display panel (self-luminous display) offer advantages of being slim, lightweight, and low-power-consumption, and have been finding increasingly wide application. For application in cellular phones, digital still cameras, and the like, however, such display devices are still to attain lower power consumption.
There have been developed RGB-type organic EL display devices having R, G, and B color filters bonded to a white light emitting material. An RGB-type organic EL display device includes, for each of its R, G, and B unit pixels, an organic EL element. In an RGB-type organic EL display device, when light passes through the color filters, part of the light is absorbed by the color filters. This results in poor light use efficiency, hampering further lowering of power consumption.
Under these circumstances, the applicant of the present application has developed, and has filed patent applications for, RGBW-type organic EL display devices (self-luminous display devices) that permit further lowering of power consumption. An RGBW-type organic EL display device includes, for each of its R, G, B, and W unit pixels, an organic EL element. These organic EL elements emits, for example, white light.
An RGBW-type organic EL display device includes a display panel composed of, as shown in FIG. 24, an array of a large number of dots, each composed of four, namely R, G, B, and W unit pixels. Three of these four unit pixels have color filters of three primary colors, for example, R (red), G (green), and B (blue), arranged thereat; the fourth unit pixel has no color filter arranged thereat to serve to display white (W).
Having no color filter arranged thereat, the unit pixel for displaying white exhibits extremely high light use efficiency. Accordingly, for example, when white is displayed, it is displayed not by making the unit pixels for displaying R, G, and B emit light but by making the unit pixel for displaying white emit light. This helps greatly reduce power consumption.
If the RGB-signals-to-W-signal conversion rate (the proportion in which RGB signals are converted into a W signal) is 100%, as much of the RGB signals as possible is converted into the W signal, and thus the high-efficiency W pixels (the pixels for displaying white) are made the most of, achieving the lowest power consumption. In a case where RGB signals are each an eight-bit digital signal, and when they all have a value of 255 (assuming that an increase in this value means an increase in brightness), if the RGB-signals-to-W-signal conversion rate is 100%, for example, as shown in FIG. 25, the RGB pixels emit no light at all, and instead the W pixels alone emit light at their maximum level, thereby displaying white.
JP-A-2001-109423 (hereinafter “Patent Publication 1”) discloses an RGB-type display device provided with means for controlling the signals applied to adjacent pixels such that the sum of the brightness of the pixels adjacent to a defective pixel equals the brightness that the defective pixel would produce were it not defective.
JP-A-2002-189440 (hereinafter “Patent Publication 2”) discloses an RGB-type display device provided with: a correction data storage portion that stores correction data prescribed according to input signals; and a correction processing portion that, when a defective pixel is found, determines correction data based on input signals and, by using the correction data, corrects the input signals to the pixels around the defective pixel.
Usually, the RGB-signals-to-W-signal conversion rate is set equal (for example, 100%) over the entire the display panel. From the viewpoint of reducing power consumption, it is preferable that the RGB-signals-to-W-signal conversion rate be set as high as possible. If there is a defect among W pixels for displaying white, however, as shown in FIG. 26, when white is displayed, the defect appears as a very conspicuous black spot (indicated by numeral 50 in FIG. 26). This not only degrades the display quality of the display panel, but also increases the incidence of defective panels, leading to a low yield.
The technologies disclosed in Patent Publications 1 and 2 mentioned above are aimed at simply increasing the brightness of pixels around a faulty (defective) pixel, if any, in an RGB-type display device, and therefore cannot be applied, as they are, to an RGBW-type display device where consideration needs to be given to, among other factors, the RGB-signals-to-W-signal conversion rate. Incidentally, in an RGB-type display device, even if a pixel is defective, when white is displayed, it is only a single R, G, or B pixel that fails to emit light. Thus, with no black spot appearing, the defect is comparatively inconspicuous.